In wide area communication networks, because of the relatively large uncertainty and considerable changes in the optical signal propagation delay, the packet arrival times must be continuously synchronized at the inputs of a synchronously-operated packet switch. One example of such an optical switch is described in IEE Electronic Letters, 13th August 1992 and is titled `Staggering Switch`: An Almost-all Optical Packet Switch, by Z. Haas, which is incorporated by reference herein.
Previously proposed schemes to provide such packet synchronization rely on a plurality of delay devices located at the input to the optical packet switch. Each device provides a delay which is a fractional part of a packet transmission time, so that substantially any value of required delay may be generated to compensate for the difference between the packet arrival time and the beginning of a local time slot in the switch. Such delay devices are typically fabricated Using fiber delay lines in combination with 2.times.2 Lithium Niobate optical modules such as Type Y-35-8771 manufactured by the GEC-Marcone Company of Baddow Chelmsford, Essex England.
The problem with the above synchronization scheme is the resulting relatively large power penalty incurred due to the multiple coupling loss between the optical modules and the optical fiber delay lines(i.e., the optical signal travels several times in and out of the Lithium Niobate wafers.)
Accordingly, there is a need for a technique to continuously synchronize the optical packet arrival times with the local time slots of a synchronously operated optical packet switch and that results in a minimum power penalty and cost.